We introduce XPORT, a profile-driven distributed data dissemination system that supports an extensible set of data types, profile types, and optimization metrics. XPORT efficiently implements a generic tree-based overlay network, which can be customized per application using a small number of methods that encapsulate application-specific data filtering, profile aggregation, and optimization logic. The clean separation between the "plumbing" and "application" enables the system to uniformly support disparate dissemination-based applications. We first provide an overview of the basic XPORT model and architecture. We then describe in detail an extensible optimization framework, based on a two-level aggregation model, that facilitates easy specification of a wide range of commonly used performance goals. We discuss distributed tree transformation protocols that allow XPORT to iteratively optimize its operation to achieve these goals under changing network and applicati...